[Elecraft] [ELECRAFT] KPA500 NEW OWNER QUESTIONS.......

[K9MA]

Many years ago, I built a tube amplifier with what I thought was a 
fairly sophisticated ALC circuit. I could never get the ALC loop to be 
stable. I know a lot more about control systems now, but I still don't 
know how to get ALC around an amplifier to work, and apparently neither 
does anyone else. What I don't understand is why it's so hard with an 
external amplifier, as every transmitter has ALC for its internal 100 W 
amplifier, and that works fine. Why the same design doesn't work with an 
external amplifier is the mystery.

The problem with just limiting the drive power and using the 
transmitter's ALC is that, especially for solid state amplifiers, the 
required drive power can vary considerably with SWR and temperature.  
That requires either riding the power control continuously or running 
your amplifier well below rated output most of the time. (Unless, of 
course, you're running a 2.5 kW amplifier, but that kind of margin is 
expensive.) So, if anyone could figure out how to get ALC to really work 
with an amplifier, I think that would be worth paying extra for.

73,
Scott K9MA


On 2/28/2019 13:12, Bob McGraw K4TAX wrote:
> Yes, improperly or incorrectly using ALC with any amp or any 
> transceiver, for that matter,  can and usually does produce distortion 
> and splatter.   Just look at some of the signals on the bands and 
> observe the ALC overshoot which exists with many radios.   And it is 
> made worse by the addition of an amplifier in line. It isn't 
> pretty!.   Yet it has little impact on the on frequency signal as 
> heard and thus the "great signal" complements follow. But look at the 
> other factors where you will find "NOT so great signal".   These 
> points should be addressed as well.
>
> 73
>
> Bob, K4TAX
>
>
> On 2/28/2019 1:04 PM, john at kk9a.com wrote:
>> I have not used ALC with any amplifier since transceivers switched to 
>> transistor finals. From what I have read on this list, using ALC 
>> improperly can cause distortion.  Just be very careful with your 
>> drive level. I believe that the KPA500 can handle 100 watts in 
>> bypass, 200 watts may be pushing it. The KPA500 is a very nice amp 
>> and it is easy to use with any transceiver.
>>
>> GL,
>> John KK9A
>>
>>
>> JIM LAGESON N0UR wrote
>> _Thu Feb 28 13:07:27 EST 2019_
>>
>>
>> -------------------------
>>
>> I have never owned an amp before and recently put together a KPA500. All
>> seems to be working well, but I have a few questions. I am using with a
>> IC-7300.
>>
>> How important is the ALC cable? I notice it is not included in the Basic
>> Cabling Diagram in the manual but is discussed later in the manual.
>>
>> If I were accidently to run 100 watts into the KPA500 will the PWRIN HI
>> Hard Fault/STBY protect itself before any damage is done. Would ALC 
>> protect
>> me from that?
>>
>> Is it standard procedure to keep the KPA500 in line when turned off 
>> and not
>> in use? I see you may run up to 200 through the KPA500 in STBY.
>>
>> Is there any concerns or settings on radio when running full break in 
>> on CW?
>>
>> Thanks
>> Jim-N0UR ml


-- 
Scott  K9MA

k9ma at sdellington.us